In a number of situations, it is useful to convert the motion of an actuator to a reduced or smaller motion, e.g., to achieve very fine changes or adjustments in position. One area in which such motion reduction may be useful is for adjustment, calibration, pointing, focusing and the like, of various technical or scientific instruments including interferometers and telescopes, particularly space-based telescopes. In the case of telescopes, the fineness or precision with which mirrors, mirror segments or other optical components must be positioned may be substantially finer than the step size with which an actuator, in a particular application, may be moved. Although actuators are of various types and are available with a variety of step sizes or precisions, there are often other constraints limiting the types of actuators available, including constraints on the size, weight, cost, suitable environment, or other performance characteristics of an actuator. According, in many situations, it is desired to use an actuator which has movement components or steps of a given minimum size but to achieve positioning of a telescope mirror segment or other optic with a precision which is finer than that of the actuator. These problems can be particularly acute in the case of a space-based telescope because of the tight constraints which weight and reliability place on actuator components. Accordingly, it would be useful to provide a device for reducing motion of an actuator suitable for technical or scientific instruments, preferably suitable for a space-based telescope or other instruments. Preferably with relatively low weight and size.
Many scientific instruments require operation at low temperatures, such as cryogenic temperatures, e.g., less than about 70 Kelvin. Although motion reduction devices are known, such as reduction gear trains, many such devices are unsuitable for use at low, e.g. cryogenic, temperatures. Among other difficulties, many previous motion reduction devices, such as gear trains, had unsuitable effective thermal conductivities such that temperature differentials between gears or other parts could reduce reliabilty, linearity of performance, or could limit the precision or fineness of adjustment. Accordingly, it would be useful to provide a reduction device which reduces the occurrence of or effect of temperature differentials and preferably which is suitable for operation at low, e.g. cryogenic, temperatures.
Many previous reduction devices included a relatively large number of relatively-moving separate parts (such as parts which are meshed or hinged with one another). Because of the potential for failure of such separate parts, as well as the interference with thermal conduction between separate parts, both of which can be particularly disadvantageous in space-based telescopes or other instruments, it would be advantageous to provide a motion reduction device which reduced or eliminated the need for meshing or hinging of separate parts in at least portions of the motion reduction device.
In some motion reduction devices, the degree of fineness of adjustment is achieved at the price of an unacceptable reduction in the range of motion of the device. In some reduction devices it was difficult or impossible to provide for coarse adjustment in addition to the fine adjustment made possible by the reduction device. Accordingly, it would be useful to provide a reduction device which provides a relatively fine adjustment throughout a relatively large range of motion, preferably with a substantially constant or linear reduction ratio, and/or which allows for coarse adjustment as well as fine adjustment of position.